1. Field of the Invention
The invention relates to an electrical switch as claimed in the precharacterizing clause of patent claim 1.
2. Description of Related Art
Electrical circuits which are arranged on a board have a wide field of use, for example in controllers, domestic electrical appliances or electrical tools. In particular, circuits such as these which are used for driving an electric motor in an electrical tool are arranged together with the board in the housing of the switch for the electrical tool.
An electrical circuit arrangement such as this has electrical and/or electronic components. The components are arranged on a mount substrate, with the conductor tracks for electrical connection of the components likewise being located on the mount substrate. A switch for an electrical tool, in particular for an electrical tool which is powered by a rechargeable battery and in whose housing the mount substrate of the drive circuit is accommodated, is disclosed, for example, in DE 41 14 854 A1. The mount substrate comprises a printed circuit board, for example based on hard-paper or FR4 technology, or else is a ceramic panel.
During operation of the electrical circuit arrangement, heat is produced in the components. These heat losses must be dissipated and this is done via the printed circuit board and the heat sink, in order to prevent thermal damage to the components, and hence destruction of the surface arrangement. It has been found that the printed circuit boards limit the effective dissipation of the heat in the case of circuit arrangements with relatively high heat losses. Particularly in the case of electrical switches for high-power electrical tools, in which a circuit arrangement is arranged for controlling the rotation speed, or for torque disconnection or the like in the housing of the switch, this has resulted in corresponding adverse effects, and even to premature failure of the switch. This problem is particularly relevant to electrical tools which are powered by rechargeable batteries where high currents flow through the switch.
An electrical switch for electrical tools having a housing which is formed from two housing halves, with one housing half being produced from metal, is also known from DE 100 19 471 A1. An electrical circuit arrangement is located on a mount substrate in the interior of the housing. The mount substrate rests against the housing half that is composed of metal, so that this housing half acts as a heat sink. However, since the mount substrate is in turn composed in a conventional manner of ceramic material, plastic or the like, the dissipation of the heat losses is also restricted in this case.
Finally, a voltage regulator for a generator in a motor vehicle is disclosed in DE 36 29 976 A1. The voltage regulator is arranged on a mounting plate, as a hybrid circuit composed of various components and a power semiconductor. The mounting plate is composed of highly thermally conductive material, for example steel, aluminum or copper, and has a thin, electrically insulating coating. Since the mounting plate is in the form of a metal part, this ensures improved dissipation of the heat losses. However, the physically large voltage regulator for the motor vehicle does not provide any information relating to the arrangement of a metallic mounting plate in a physically small housing for an electrical switch.